dispatch: move findrepo to cmdutil

localrepo: don't search from path All current callers already pass in the repo root. This normalizes things a bit. Now all repo types take a direct path to repo root and only the command line interface (or the dispatcher) searches from the current directory.

dispatch: use the repo path found by early parsing This lets us simplify things a bit.

dispatch: parse and apply -R early This allows us to use extensions specified in .hg/hgrc. Unfortunately, this requires us to parse that file twice, but performance impact on the version command appears to be less than 1%.

dispatch: parse and apply cwd opt early

dispatch: rename variables after code motion

dispatch: hoist debugging hook to runcatch

dispatch: move dispatching code to cmdutil

dispatch: move runcommand to cmdutil

dispatch: pull final command execution into its own function